With the release of Runescape 3, strength is not worth training anymore if you already have 90+. It's good you have 99 defence because defence now applies to the whole combat triangle, which means defence provides defence against magic, melee and ranged. The Runescape 3 update focuses on the combat triangle, so I suggest becoming a hybrid/tribrid. Do this by training up magic and/or ranged. Regarding your original question, if you really wanted to train strength, train on deadly red spiders - located in Varrock sewers. Good luck. :)
